1. Field of the Invention
The present invention relates to an apparatus and method for venting hydrogen from an electrolytic cell and, more particularly, to an apparatus and method for venting hydrogen from a system producing hypochlorite by electrolysis.
2. Description of the Related Art
Various techniques are available for disinfecting a water supply. Common among these methods is the addition of chemical disinfectants, primarily oxidants, to reduce the microbial content of water. Chlorine, in various forms, is a widely used oxidant, and several techniques exist for introducing it into a water supply. For example, chlorine gas may be injected directly into water, or a solution of hypochlorite (OClxe2x88x92), the anion of hydrolyzed chlorine, may be added to the water. Hypochlorite solution may be produced on site and added on demand to the water being treated. The ability to produce a hypochlorite solution locally makes this technique particularly attractive and economically efficient.
One method of producing hypochlorite is through the use of an electrolytic cell. One or more electrolytic cells, including anodes and cathodes, are housed within a device called an electrolyzer. A brine solution, that is, a solution containing dissolved chloride, and typically 3% w/w chloride, is fed to the electrolyzer. The application of current to the electrolytic cell containing brine solution results in an electrolytic reaction that produces hypochlorite that may then be transferred to a water supply at a concentration that is capable of reducing the microbial content of the water to an acceptable level.
One commercially available apparatus for producing hypochlorite in this manner is the OSEC(copyright)-LC hypochlorite production system (United States Filter Corporation, Palm Desert, Calif.). Such a system 100, as illustrated in FIG. 1, includes an electrolyzer 20 and requires a source of brine 40 which may be a synthetic source such as a salt saturator or a natural source such as sea water. Brine supplied by a salt saturator is typically diluted by mixing with water in the electrolytic cell. As the efficiency and useful life of electrolytic cells may be reduced by the presence of undesirable dissolved constituents in the water and/or brine supply, synthetic brine sources are often used and pretreatment devices are employed to upgrade the water supply prior to its use. Such pretreatment devices often include a water softener 110 to reduce hardness in the water feeding the salt saturator 40 and the electrolyzer 20.
To produce a hypochlorite solution, typically a solution of sodium hypochlorite, a brine solution is fed into an electrolytic cell 29 where electrolysis takes place. The electrolytic cell contains cathodes and anodes in quantity and size to support the electrolytic current required to produce a supply of hypochlorite at a rate adequate to supply the particular water system with which the apparatus is being used. To produce a brine of appropriate concentration, a concentrated chloride solution is typically pumped into the electrolytic cell from the salt saturator 40 and is mixed with a regulated flow of water to result in a 3% brine solution. The regulated flow of water may be provided through flow controller 47 and may be monitored via flow indicator 46. The resulting hypochlorite solution is transferred through a product outlet 23 into a tube that leads to a storage tank 50. From the storage tank 50, the hypochlorite solution may be pumped into the water supply at a rate and concentration adequate to supply the desired concentration of chlorine.
In addition to producing hypochlorite from the brine solution, the electrolytic process results in the production of hydrogen gas, as a byproduct. This combustible gas passes with the product through conduit 24 into the product storage tank where it separates from the liquid product. To remove hydrogen gas, the hypochlorite storage tank 50 is provided with a vent 51 that allows the hydrogen, under atmospheric pressure, to exit the system. An air blower 120 may also be connected to the storage tank in order to provide a flow of air to the interior of the storage tank and thereby aid in venting of the hydrogen from the storage tank 50. Depending upon the efficiency of the system, from about 5 to about 15 cubic feet of hydrogen, at atmospheric pressure, are produced for each pound of chlorine that is generated by the system, and some hypochlorite production systems may produce upwards of 2,000 pounds of chlorine (as hypochlorite) per day. Typically, hypochlorite production systems are provided with electronic controls to monitor the operation of the electrolytic cell as well as the water softener, salt saturator, sodium hypochlorite storage tank, and any other modules that may be included. The hypochlorite is typically made in a batch process, and the electrolytic cell is de-powered once the hypochlorite storage tank 50 is fill. Once the electrolyzer 29 has been turned off, it is often desirable to drain the electrolytic cell to inhibit galvanically induced corrosion of the metal components in the cell, and to facilitate this, the cell of the electrolyzer is often fitted with a cell drain 25 that is used to empty the electrolyzer either to waste or to the product storage tank 50.
The present invention is directed to an apparatus and method for venting hydrogen from an electrolytic cell. The apparatus includes an electrolyzer having an electrolyte inlet and a product outlet, at least one electrolytic cell positioned in the electrolyzer, a vent, and a non-combustible gas source in fluid communication with the electrolyzer.
In another embodiment, the apparatus includes an electrolyzer having an electrolyte inlet and a product outlet, at least one electrolytic cell, a vent, and a vacuum source in communication with the vent.
In another embodiment of the invention, a system for producing hypochlorite is provided. The system includes an electrolyzer having at least one electrolytic cell in fluid communication with a product outlet, a brine inlet, a non-combustible gas source, a brine source, a storage tank and a vent.
In another embodiment, the present invention provides for a method of producing hypochlorite. The method includes the steps of supplying a brine solution to an electrolytic cell in an electrolyzer, producing hypochlorite ion and hydrogen gas in the electrolyzer, introducing a non-combustible gas, diluting the hydrogen in the electrolyzer to a concentration below a combustible limit, and venting the diluted hydrogen from the electrolyzer.
In another embodiment, the present invention provides for an electrolyzer. The electrolyzer has an electrolyte inlet and a product outlet as well as an electrolytic cell positioned in the electrolyzer. A retention area is positioned within the electrolyzer and is downstream of the electrolytic cell.